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Tuesday, December 2, 2014

Help! There's a lump on my pet! (Part II)

Tira isn't too impressed.

So there's a lump on your pet. In yesterday's post we discussed how veterinarians work out what that lump is. Today we're going to talk about staging and surgery. When it comes to cancer, the two important things you need to know boil down to this: what is it? and where is it? They are deceptively simple questions. Sometimes it takes a number of tests to determine the answers.Why
is surgery required? Surgery is performed for a number of reasons.
Sometimes the aim is to achieve a diagnosis, by obtaining a biopsy and
exploring the extent of local disease. Often the aim is to cure the patient –
by removing all abnormal tissue. In human patients, 60% are cured of cancer by
surgery alone1. In cases of
advanced or aggressive disease, surgery may be means of relieving pain and
improving quality of life (palliation). Surgery may be combined with chemotherapy
or radiotherapy to ensure that microscopic disease is not left behind.

What
planning is required and why? Surgery is similar to
medication in that we can think of surgery like a “dose”. If we under-dose the
patient by failing to remove enough tissue, we potentially leave cancer cells
behind. If we over-dose the patient, that is, remove too much tissue, we may
have complications including delayed wound healing, poor functional outcomes
(for example, if too much muscle is removed) or poor cosmetic outcomes. To
determine the correct dose, we need to know what kind of tumour we are treating
and the likely behaviour of that tumour.

What
do we need to know to plan surgery? Firstly it is important to
know what the tumour is. A biopsy is sent to a pathologist for evaluation of
cells (cytology) or tissue (histopathology). In most cases this provides
information on the type of tumour and the grade, which can in turn help us
predict how that tumour will behave (for example, is it more likely to spread
to distant sites in the body (metastasize)).

Secondly, we need to know
where the tumour is – is it isolated to a single anatomical site, such as a
lump, or is it present elsewhere in the body, for example metastases in the
lymph nodes or lungs. Knowing the location and the extent of the tumour is
important in determining the most effective treatment. The process of finding
this out is called staging and may involve blood tests, chest x-rays, ultrasound,
sampling lymph nodes and even advanced imaging with CT and MRI. This helps us
to determine whether and how we can remove the entire tumour, and what
additional treatment may be required.

A chest x-ray. This dog has concurrent congestive heart failure and some suspicious looking areas in the lungs.

Can’t
you just remove as much of the tumour as possible? Unfortunately
this approach doesn’t work well. It can be helpful to think of cancer like a
crab sitting on or in the body1. If we remove the
biggest part, the body of the crab, but leave the legs behind we’re in trouble.
The body of the tumour is often the slowest growing part, while the edges of
the tumour (the legs) are the most invasive. If we leave these behind, we may
actually be selecting for the most aggressive parts of the tumour – and leaving
ourselves without healthy normal tissue to close the wound.

What
factors influence the outcome? Aside from the general
health of your pet, the best outcomes are associated with slow-growing tumours
that have discrete boarders and can be isolated from underlying tissue, small
tumour size and a low histologic grade. If we are aiming to cure, our best
chance for a cure is the first operation. Surgery may be less successful if the
tumour is recurrent, is poorly defined, or has a history of rapid growth1.

It is often said that a chance to cut is a chance to cure for a reason. (In this case its also a chance to sample an awesome guinea pig cake).

Why
do we submit the lump for pathology after removal? Following removal, there are
two key reasons for having a pathologist assess the lump. First, the diagnosis
can be confirmed. Secondly, the pathologist can assess the margins – that is
the amount of normal tissue removal along with the lump. Clean margins consist
of healthy tissue without neoplastic cells. “Dirty” margins have evidence of cancer
cells or microscopic disease.

Are
additional treatments required? This depends on the tumour
type and stage. In many cases, the tumour is removed and that is the end of the
story. If margins are “clean”, there may be no further treatment required. If
margins are “dirty”, further surgery may be required. This should be performed
as soon as possible to remove the entire previous surgery site. In some cases,
chemotherapy or radiotherapy prior to or following surgery may improve the
outcome for your pet.

Veterinary Ethics: Navigating Tough Cases

WARNING

All images and content on this site are copyright Anne Fawcett unless stated otherwise and should not be reproduced without written permission. Please be aware that some surgical and clinical images are used on this site.